Libovsdb docs; client and server side indexing

[tssurya]

What would you like to see added/updated/deleted in our docs?

Libovsdb docs; client and server side indexing are missing in contributor/developer docs.

Why is this needed?

I think its nice to have info on

1. client side indexing
2. server side indexing
3. how ovnkube uses libovsdb
4. moving forward all new OVN Constructs must leverage dbindexes
5. details of indexing nuances of each ovn object in ovnkube etc

because moving forward as we convert all objects to using dbindexes we might not remember how it works for each case.